1. Field of the Invention
This invention relates to an optical instrument for facilitating in the observation of surface engravings located on an optical lens.
2. Description of the Prior Art
Conventional multi-focal lenses are formed by joining two or more sub-lenses of different optical power together to form a final composite lens. For example a composite lens could be formed from two different sub-lenses having different optical powers. Such a lens, commonly called a bifocal lens, usually has a line formed between the two sub-lenses. Therefore, these lenses have clear reference points to aid an optical practitioner in positioning the lens when it is worked on. Furthermore, since the optical power of each sub-lens is constant within the particular sub-lens, the power of each sub-lens can be easily measured.
In order to remove the line formed between sub-lenses of differing optical powers, it has now become somewhat common to mold the front surface of a multi-focal lens in such a way as to form a gradual set of curves from different areas of the lens. A variation of curves results in refractive power variation from distance to near corrections without the need for specific power segments or lines. Such a lens is commonly referred to as a progressive addition lens. The lines formed in previous multi-focal lenses were not considered aesthetically pleasing and, in fact, the lines formed in the lenses could interfere with the vision of the user. However, with progressive addition lenses, visual correction from one refractive power zone to the next is smooth. For at least this reason, progressive addition lenses are considered more comfortable and have been favorably accepted by users. In general, this new lens design presented a large technological advancement over multi-focal lenses and, as a result, tens of millions of progressive addition lenses are being worn around the world today, with more than ninety types produced by more than two dozen manufacturers.
Unfortunately, unlike lined or conventional multi-focal or bifocal lenses, progressive addition lenses to not have obvious reference points for positioning each lens during processing or inspection by an optician or optical technician. Furthermore, since the front surface of a progressive addition lens is aspheric, it is very difficult to determine the power of the lens or its optical center with manual or automatic lens reading instruments currently available in the optical industry.
In an attempt to overcome this problem, it has become commonplace for manufacturers of progressive addition lenses to engrave informational markings on the front surfaces of these lenses. Such markings typically include geometric symbols indicating various properties of the lens, such as the horizontal centerline, optical power, manufacturer, specific model and other pertinent information. These engravings typically vary from bold to extremely faint. To further complicate matters, the optical qualities of the engravings on plastic and glass lenses are different. Since the introduction of progressive addition lenses, manufacturers of such lenses have varied the engraving depth, as well as the particular locations of the markings so as to be unobtrusive and unnoticeable to the wearer. Unfortunately, available devices used to observe these markings are not considered satisfactory such that locating and identifying the markings on a wide range of lenses has generally represented a time consuming and arguous task. This problem is particularly prevalent when attempting to read rather old lenses which may be scratched and/or coated.
Based on the above, there exists a need in the art for an optical instrument for facilitating the observation of surface engravings located on an optical lens. More particularly, there exists a need for a device which will allow even faint engravings on an optical lens to be readily viewed by an optical practitioner. In addition, there exist a need for such an optical instrument which can be used in viewing engraving in both plastic and glass lenses. Furthermore, there exists a need for an optical instrument which is simple in construction and is easily adapted for use with little or no special training.